1. Field of the Invention
This application is a 371 of PCT/EP94/00370 published Feb. 9, 1994.
The invention relates to a combination of a heated lambda probe with an abrupt or binary sensor characteristic and an additional heated lambda probe for determining the lambda value in a gas mixture, for example in exhaust, preferably from internal combustion engines.
2. Description of the Prior Art
Lambda probes are known (DE-A-41 09 560) and operate as binary lambda probes which merely determine whether the value above or below the lambda value is equal to one.
Since known lambda probes are subject to drift, i.e. the measured lambda values change during operation or as a result of aging, two-probe systems are known (DE-OS 24 44 334, DE-OS 223 04 622, U.S. Patent No. 4,739,614).
In addition, a combination composed of two probes is known (DE-A0-41 35 254), in which one probe is located upstream of the catalyst itself and the other is located beyond the catalyst in the flow direction, with one of the two probes serving to detect changes in the measurement behavior of the other and to compensate for them.
In the known combination composed of two lambda probes, however, errors occur because of the considerable distances between the two lambda probes.